Abstract : In our environment, we can frequently identify phenomena that can be well studied under single input / single output representation (from now on SISO), for example in the fields of Biotechnology (case of the study of Landfills) or Geosciences (propagation of water through cracks), when researchers fill a tracer in an determined area. In the first case, many reactions take part in the area, but since a landfill is usually huge, it is diffcult to know what happens in the inside of it. The only thing that we know is that the re-circulation leachate increases the bio-reaction rates since it improves the system mixing. So, we would like to study what happens if we put an inert substrate in the leachate to understand the behaviour of this fluid. In the second case, it could be interesting to study how the water or any source propagates in an area, in order to know for instance what could happen in case of a natural disaster as a big rain or a melting of glaciers and this way to know where to install an urban settlement. So, the idea here is as before, to put an inert substrate in a source and to measure the output response. The motivation for this work is to characterize these two phenomena exposed above, assuming that initially biological interaction does not happen or considering an inert chemical tracer. These phenomena can be well modelled as a SISO compartimental system with a large network of many tanks, to capture the spatial inhomogeneity and the complex routes of water through the media.